Polyesters have been characterized as heterochain macromolecular compounds that possess a plurality of carboxylate ester groups as components of their skeletal structure as distinguished from other ester-containing polymers, such as cellulose esters, poly(acrylates) and poly(vinyl esters), which have carboxylate groups forming part of pendants from the skeletal structure. Polyesters have found wide utility, being used as fibers, films, plasticizers and polyurethane intermediates to name but a few applications.
Although many reactions are possible for the synthesis of polyesters, conventionally the polyesterification of dicarboxylic acids or their functional derivatives with diols followed by a polycondensation reaction is most widely utilized.
Despite being suitable for many applications, polyesters have been treated with a variety of additives to enhance their physical properties. For example, silicones have been used in combination with polyesters to improve lubricity, water repellancy and softness of polyester articles. Traditionally, silicones have been applied topically to the finished polyester; see, for example, U.S. Pat. No. 4,105,567. Topical treatment of polyester and other fabrics, however, results in short-term improvement in fabric properties. Over time and repeated washings, topically silicone-treated polyesters lose their effectiveness as the silicone dissipates. Therefore, it is highly desirable to permanently incorporate the silicone into the polyester resin such that permanent improvement in properties can be realized.
Silicone-modified polyesters which are advantageously used in fibers are described in U.S. Pat. Nos. 4,640,962; 4,766,181; and 4,758,637. These patents disclose silicone-modified polyester resin having discrete domains within the polyester matrix. During melt spinning and cold drawing, the domains undergo migration to the surface of the resulting polyester fiber so as to provide a silicone-sheathed polyester fiber. These patents require that a copolymer domain of a controlled size be formed. In addition, the patents specify that the reactive polysiloxane end groups which are incorporated in the polyester backbone cannot be hydroxy-capped.
There continues to be a need for polyester resin having improved properties such as, in particular, hydrophilicity, for use in fibers and films. Cotton and other cellulosic fibers have the ability to "wick" or draw perspiration from the body resulting in a comfortable feeling for the wearer. In contrast, articles made with a high level of synthetic fibers such as polyester fiber cannot draw moisture from the body and result in a "clammy" feeling to the wearer. Therefore, hydrophilic polyester fiber is desirable because such fiber would behave more like cotton and articles made therefrom would be cooler and thus more comfortable to wear.
Similarly, hydrophilic polyester film is desirable since water would wet the surface better than unmodified polyester film. Improved wetting is important in cleaning the surface of the film.
Accordingly, it is desirable to provide polyester resin which is hydrophilic and which can permanently retain its hydrophilic properties during the useful life of products made therewith.